Alumina sintered articles have heat resistance, chemical resistance, and plasma resistance, and also have a low dielectric dissipation factor (dielectric loss or tan δ) in a high frequency range. Thereby, alumina sintered articles is used for members of a semiconductor manufacturing apparatus and members of a apparatus for manufacturing LCD panels such as members for use in high frequency plasma apparatuses and the like.
Since such members of semiconductor or LCD manufacturing apparatuses contact with highly corrosive cleaning gases comprising halogen and plasma thereof, alumina sintered articles with a high purity of 99.0 mass % or more may be used as the members.
On the other hand, dielectric loss of alumina sintered article having less impurities and additives may be high. In this case, the transmission rate of high frequencies in the megahertz band of the alumina article may be decreased, energy loss may be increased or heat generated may break the alumina article.
Alumina sintered articles with a certain range of contents of SiO2, CaO, and MgO as sintering aids may result in low loss, thereby yielding alumina sintered articles with improved high-frequency dielectric properties as well as low firing temperatures.
The alumina sintered article comprises 99.8 to 99.9 mass % of alumina and a grain boundary comprising SiO2, CaO, and MgO at a predetermined ratio, and has a Q value of 10000 or more and a dielectric loss of 0.0001 or less at a frequency of 8 GHz.
However, the alumina sintered articles have high dielectric loss in the megahertz band, and for example, when the alumina sintered articles are used for members for high frequency plasma apparatuses for semiconductors, and the like for use at high frequencies in the megahertz band, the transmission rate of high frequencies in the megahertz band will be decreased, thereby leading to occurrence of problems such as increase in energy loss or breakage of the member due to heat generation.
An alumina sintered article may comprise anisotropic crystal grains comprising a composite oxide with Al and at least one of La, Ca, Sr, Ba, Sm, Nd, and Ti to improve oxidation resistance and mechanical properties.
The alumina sintered article may comprise alumina crystal grains with an average crystal grain diameter of 10 μm or less, and 1 to 20 volume % of anisotropic crystal grains with a longitudinal length of 20 μm or more with respect to the total amount thereof, thereby resulting in improved fracture toughness and improved strength at a room temperature.
However, the alumina sintered article has low dielectric loss. In this case, the transmission rate of high frequencies in the megahertz band will be decreased when used at high frequencies of the megahertz band such as used for members of plasma apparatuses for semiconductors and the like.